GB781805A - Process for the production of concentrated acrylic acid - Google Patents

Abstract

Concentrated acrylic acid is obtained by reacting in the presence of an excess of water and in the presence of a solvent, acetylene, nickel carbonyl, carbon monoxide and an acid sufficiently stronger than acrylic acid to prevent the formation of nickel acrylate, the solvent being at least partly miscible with water, immiscible with a concentrated aqueous solution of the nickel salt formed, and capable of forming, together with water, an azeotropic mixture boiling below 140 DEG C., and the quantities of solvent and water being so related that a part of the water takes up the nickel salt out of the reaction mixture so as to form a highly concentrated solution of the nickel salt and the remainder of the water forms with the solvent and acrylic acid a mixture in which the amount of water present based on the weight of water and solvent present does not exceed the water content of the azeotropic mixture of water and solvent at atmospheric pressure, and distilling off the azeotropic mixture of water and solvent. Specified solvents are acetonitrile and ketones, e.g. methyl ethyl ketone, pentanone-3, pentanone-2 and 3-methyl-butanone-2. The azeotropic mixture of solvent and water which is distilled off from the mixture may be used again in a further charge. In a typical example: (1) a solution of methyl ethyl ketone, water, acrylic acid and hydroquinone is warmed to 30 DEG C. in a vessel provided with a reflux condenser, stirrer, thermometer and gas inlet tube and nickel carbonyl is added. After further heating to 48 DEG C. an aqueous solution of hydrochloric acid, further nickel carbonyl and acetylene are added and after some reaction has occurred carbon monoxide is added in such amount that the proportion of carbon monoxide from nickel carbonyl to carbon monoxide gas is 63:37. The reaction temperature is maintained at 50 DEG C. by cooling and on completion of the reaction the mixture is clear and consists of two layers, the lower layer comprising an aqueous solution of all the nickel chloride formed together with traces of acrylic acid whilst the upper layer contains acrylic acid, methyl ethyl ketone and water. The upper layer is fractionated in a Vigreux column at a bath temperature not exceeding 125 DEG C., the distillation being carried at atmospheric pressure until about half the contents of the flask had passed over and then continued at reduced pressure until over 90 per cent of the water which was present in the upper layer is in the mixture of solvent and water which distils over, only small amounts of acrylic acid being present in this mixture. The contents of the flask are then further distilled under reduced pressure to recover acrylic acid which solidifies on cooling in an ice-cooled refrigerator. Two other examples (2) and (3) are given in which the same solvent and acid are used as in (1). In (2) the aqueous azeotropic methyl ethyl ketone solution from a previous operation of the process is used again in the charge mixture whilst in (3) the process is carried out in a vertical reaction tube fitted with a drain cock at the bottom and provided with a reflux condenser, thermometer, stirrer and gas inlet tube. The tube initially contains methyl ethyl ketone, water and hydroquinone and aqueous hydrochloric acid, acetylene, nickel carbonyl and monoxide are then added slowly. The lower layer which is formed and which comprises a concentrated nickel salt solution is constantly withdrawn during the process whilst the acrylic acid is recovered by fractionation of the upper layer as in (1) above.